These studies are designed to develop improved methods for detect-ing and treating malignancies. Our group performs preclinical evaluation of antibodies that appear to be promising after initial screening by various laboratories at the National Cancer Institute and develops these antibodies for clinical application. The clinical trials evaluating their pharmacokinetics and dosimetry are performed by our group. A collaborative radioimmunotherapy trial with Dr. Waldmann (Principal Investigator) in which we used humanized anti-tac monoclonal antibody, is ongoing. Imaging studies comparing the use of Tc-99m anti- CEA Fab (FDA approved) and F-18 deoxyglucose in patients with previous history of colorectal carcinoma and rising CEA with-out evidence of disease by conventional radiographic modalities are ongoing. We have characterized the fate of alpha emitting labeled antibody once modulation and internalization occur, as part of their preclinical evaluation. We have begun preliminary studies evaluating pretargeting of antibodies for tumor therapy.